In recent years, suppressed electrostatic capacitance changes with temperature, as well as reductions in leakage current have been required for dielectric ceramics for use in capacitors intended for middle to high pressures (for example, direct-current rated voltages from 1 kV to 6 kV). The leakage current i is defined by the following formula (1) with the frequency f, capacitance C, and voltage V.i=2πfCV  Formula (1):
From the formula (1), it is determined that the leakage current is increased with the increase in capacitance value C. Therefore, in particular, reductions in leakage current have been required for capacitors intended for middle to high pressures, which are high in capacitance value, and there is a need to improve dielectric ceramics for use in the capacitors in terms of insulation property.
Conventionally, the dielectric ceramic described in Patent Document 1 is known as a material that undergoes a small change in electrostatic capacitance with temperature. This dielectric ceramic is composed of a fired mixture of 100.0 parts by weight of a basic constituent and 0.2 to 5.0 parts by weight of an additive constituent, and the basic constituent is composed of a substance represented by (1−γ−η) (Bak−(x+y)MxLy)OkTiO2+ηJZrO3+γ(R1−zR′z)O3/2+αAO5/2+βD (M is Mg and/or Zn, L is Ca and/or Sr, J is Ca and/or Ba, R is one, or two or more elements selected from La, Ce, Pr, Nd, Pm, Sm, and Eu, R′ is one, or two or more elements selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, A is P and/or V, and D is one, or two or more oxides selected from Cr, Mn, Fe, Co, and Ni), whereas the additive constituent has Li2O, SiO2, and MO (MO is one, or two or more oxides selected from BaO, SrO, CaO, MgO, and ZnO).
Patent Document 1: Japanese Patent Application Laid-Open No. 7-272972